The present invention relates to a vacuum sewer system comprising a sewage receptacle, sewer piping connected to the sewage receptacle by means of a discharge valve, a vacuum generating means for generating vacuum in the sewer piping, and a control mechanism for controlling the discharge valve, according to the preamble of claim 1. The present invention also relates to a discharge valve for such a vacuum sewer system according to the preamble of claim 11.
In the context of the present invention the sewage receptacle may be e.g. a toilet unit or toilet bowl, urinal, sink, wash basin, shower, etc. The sewage may be black water originating from e.g. a toilet unit or a urinal, or grey water originating from e.g. a sink, wash basin, shower, etc. A rinse water arrangement may be deployed depending upon the source of sewage.
In vacuum sewer systems, where the function of the sewage receptacle, and particularly the discharge valve, is pneumatically governed, i.e. by air/vacuum, the source of vacuum normally is the sewer piping. Vacuum for the control mechanism is often taken at a point of the sewer piping adjacent the discharge valve in the flow direction of the sewage. When the discharge valve is opened, the vacuum level is lowered due to atmospheric air entering the sewer piping.
The control mechanism functions like a three-way valve, whereby the closing of the discharge valve takes place by aeration of the same by way of the control mechanism. Consequently, the closing speed is dependent on the flow resistance of the aeration conduit.
Previously known vacuum governed discharge valves have a distinctively high noise level as the air-flow through the discharge valve is strongly choked or throttled when the discharge valve is closed.
Examples of previous attempts to lower the noise level may be found in U.S. Pat. No. 6,128,789, in which the discharge valve is closed more rapidly, EP 0 436 357 and EP 0 778 432, in which supplementary air is introduced into the sewer piping. These solutions are rather complex and provide a very limited result.